A 400-foot, 16 mm movie on the growth of mouse granulocytes was made. Multiplication and maturation of granulocytes were observed on top of the "natural feeder cells." Four successive divisions of a single precursor, presumably the promyelocytes, was filmed. A total of 3 crops of granulocytes was observed in a period of 3 weeks. Death of newly divided daughter cells was observed in the 2-week- and 3-week-old cultures. This appears to be the first motion picture showing complete maturation of granulocytes in cell cultures.